Thames Tideway ‘super-sewer’ cost rises to £4.5bn


The cost to deliver the Thames Tideway Tunnel could now be £4.5 billion, a revised estimate revealed. 

Thames Tideway Tunnel
Tideway chief executive, Andy Mitchell. Credit: Tideway.

Tideway, the company behind the 15-mile ‘super-sewer’ infrastructure, reported a c.2% cost increase since its 2021/22 end of year report. 

The major works project had, in 2014, initially been costed at around £3.5 billion. 

Tideway said the upwardly revised figure over the course of construction factored in its remaining works programme and the cost of inflation – but that the project was nearing 90% completion and is expected to be operational under Thames Water in the second half of 2025. 

“When fully operational in 2025 the new infrastructure will capture 95% of overflows from London’s sewerage network, dramatically improving the water quality of the Thames and delivering significant environmental benefits,” said Tideway. 

It added sewage overflows will begin being diverted from the Thames to the new sewer tunnel in 2024. 

Started in 2016, construction had been aimed for completion by next year, but was rescheduled owing to delays brought about by the pandemic. 

Tunnelling completed in April last year. Final stage works include critical installation and testing of connections on all the routes of the infrastructure. 


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